To increase the areal storage density of a magnetic recording device, the recording layer thereof may be provided with smaller and smaller individual magnetic grains. This reduction in grain size soon reaches a “superparamagnetic limit,” at which point the magnetic grains become thermally unstable and incapable of maintaining their magnetization. The thermal stability of the magnetic grains can be increased by increasing the magnetic anisotropy thereof (e.g., by utilizing materials with higher anisotropic constants). Increasing the magnetic anisotropy of the magnetic grains, however, increases their coercivity and therefore requires a stronger magnetic field to change the magnetic orientation of the grains (e.g., in a write operation).
Energy-assisted magnetic recording (EAMR) is used to address this challenge. In an EAMR system, a small spot where data is to be written is locally heated to reduce the coercivity of the magnetic grains therein for the duration of the write operation, thereby allowing materials with increased magnetic anisotropy to be used, and greater areal storage density to be exploited. In EAMR approach, a semiconductor laser diode is normally used as a light source and coupled to a planar waveguide which serves as light delivery path. A grating structure may be used to couple the laser light into the waveguide. Design challenges for these grating structures include improving their coupling efficiency and the difficulty in aligning a light source for high volume manufacturing processes. The coupled light is then routed to a near field transducer (NFT) by which the optical energy is provided to a small optical spot on the recording media a few tens of nanometers (nm) in size. The optical energy provided to the small optical spot generates a thermal spot in the recording media.
In order to write at higher densities, a smaller thermal spot is desired. Because the conventional magnetic recording medium typically includes lower thermal conductivity underlayers, the thermal spot is typically larger than the optical spot. Thus an even smaller optical spot is desired at higher densities. In order to obtain a smaller optical spot, optical components within the conventional EAMR system need to be scaled down to small sizes. Fabrication of portions of the conventional NFT, at such small sizes may be challenging. For example, a width of a pin section of the NFT (the “pin width”) becomes vanishingly small at high areal density. In addition, with a conventional NFT arrangement, the trailing edge of the thermal spot has a high degree of curvature, which limits the track density due to SNR degradation from the track curvature.
Accordingly, what is needed is a system and method for optimizing the trailing edge of the thermal spot in a recording media.